Recently, highly efficient and down-sized hermetic compressors with reduced noise emission have been required for refrigerating plants and the like.
U.S. Pat. No. 5,228,843 or Japanese Patent Laid-Open Application No. 2001-503833 discloses conventional hermetic compressors.
Now, a conventional hermetic compressor is described with reference to the drawings. FIG. 5 shows a longitudinal sectional view of the conventional hermetic compressor. FIG. 6 shows a partial sectional view of the conventional hermetic compressor. In FIGS. 5 and 6, enclosed container 10 encloses motor element 50 consisting of stator 3A with winding 3a and rotor 4A, and compressor element 60 driven by motor element 50. Oil 80 is stored in the enclosed container 10. Crankshaft 10A has main axial section 11 pressed to insert securely in rotor 4A and eccentric section 12 disposed in an eccentric position with respect to main axial section 11. Oil pump 13 provided internally of main axial section 11 of the crankshaft has an opening in oil 80. Cylinder block 20 having an approximately cylindrical shaped compression chamber 22 and bearing element 23 to hold main axial section 11 is disposed above motor element 50. Piston 30 is reciprocably inserted into compression chamber 22 and is coupled to eccentric section 12 via coupler 31. Suction valve 35 comprises valve plate 32 to close an end face of compression chamber 22, movable valve 33 and suction hole 34 drilled in the valve plate to communicate with compression chamber 22. Head 36 forming a high-pressure chamber is fixed opposite to valve plate 32 of compression chamber 22. Suction pipe 39 fixed to enclosed container 10 is coupled to a low-pressure side (not shown) of the refrigerating cycle to draw the refrigerant gas (not shown) into enclosed container 10. Suction muffler 40 is fixedly held between muffling space 41, valve plate 32 and head 36. First end 42 of communication passage 44 is communicated with suction hole 34 of valve plate 32. Second end 43 of communication passage 44 opens into muffling space 41, and opening 45 communicating with an interior of muffling space 41 and an interior of enclosed container 10 to open adjacent to suction pipe 39.
An operation of the hermetic compressor with the aforementioned configuration is described. Rotor 4A of motor element 50 rotates crankshaft 10A, and the rotation movement of eccentric section 12 travels to piston 30 via coupler 31. As piston 30 reciprocates in compression chamber 22, refrigerant gas flows into enclosed container 10 from the refrigerating system (not shown) through suction pipe 39. The flowed in refrigerant gas is sucked into muffling space 41 through opening 45 of suction muffler 40.
Next, the refrigerant gas flowing intermittently into compression chamber 22 via suction valve 35 through passage 44 and suction inlet opening 34 is compressed and then discharged to the refrigerating system. Here, at the time when the refrigerant gas is sucked into compression chamber 22, opening/shutting movements of movable valve 33 generate pressure pulsations in the refrigerant gas and the pressure pulsations propagate in a direction opposite to the stream of the above refrigerant gas. The pressure pulsations of the refrigerant gas attenuate and muffle in repeated expansion and contraction during the flow of refrigerant gas through communication passage 44, muffling space 41 and opening 45 in suction muffler 40 having respective different cross sectional areas.
In the aforementioned conventional configuration, however, pressure pulsations generated in the refrigerant gas by opening/shutting movements of movable valve 33 do not attenuate sufficiently. In addition, the pressure waves have large values at the passage opening 43 disposed at the end of muffling space 41. In muffling space 41, sound propagating compressional waves form standing waves for some natural frequencies by reflection. The sound pressure is high in dense portions (hereafter referred to as anti-node) of the standing waves and low in non-dense portions (hereafter referred to as node) of the standing waves. Among a distribution of the standing waves, the node is not produced at the end of muffling space 41. The problem is, therefore, that the noises do not attenuate sufficiently for some natural frequencies in the conventional art. Additionally, in the aforementioned conventional art, the refrigerant gas sucked through opening 45 is discharged to muffling space 41 having a large space capacity before being sent to communication passage 44. Here, the refrigerant gas receives heat energy from inner surfaces of muffling space 41 resulting in reduction of refrigerant gas density to cause a reduced refrigerating capacity.
Moreover, the resonance frequency of communication passage 44 that is determined by the length of communication passage 44 is difficult to adjust in the conventional art because communication passage 44 can not be extended any more. Consequently, pressure pulsations in communication passage 44 varied by the resonance frequency can not be maximized at the time just before the opening time of movable valve 33. The problem is that the volume of refrigerant gas flowing into compression chamber 22 decreases to cause a poor refrigerating capacity and efficiency.
The present invention aims to provide a hermetic compressor with a reduced noise emission in the muffling space of the suction muffler and an improved refrigerating capacity and efficiency to solve the aforementioned problems.